J 


m* 


V .  S.  I  DEPARTMENT   (  >F  AGRICULTURE, 

BlTRKAU  OF   PL  \.\T   INDUSTRY     Circular  NTo.  23. 

B.  T.  GAIXOWAY,  Chief  i. 


POTATO  DISEASES  IN  SAN  JOAQUIN 
COUNTY,  CALIFORNIA. 


W.  A.  OKTON, 

Pathologisi   i\  Charge  oi  Cotton    vnd  Truck  Diseases 
\m>  Plant  Dise  \>i:  %\  k\  i  5 . 


rON   :  GOVERNMENT   PKiMTINQ  OFFICE  :   1909 


D#CUm£nTFJ-  hfpT 


OEPOSITORY 


BUREAU  01    PLANT  INDUSTRY. 

Physiologist  and  Pathol  Bureau,  Beverlj  T    Galloway. 

Physiotogm  mid  Pathologist,  mid    Vssistani  Chief  Albert   P.  Woods. 

Laboratory  of  Plant  Pathology,  Erwin   I-'.   Smith,   Pathologist   in  Charge. 
Fruit  Disease  In  n  .  Merton  1'..  Waite,  Pathologist  in  Charge. 

Laboratory  0/   Forest  Pathology,  Haven   Metcalf,   Pathologist   in  Charge. 

■1, at   Truck  Diseases  and  Plant   Diseasi    Survey,   William   a,   Orton,   Patholo; 

Charge.  • 

Pathological  Collections  anil  Inspection    II  01  I. .   Flora    \V.   Patterson,    Mycologist    iu  Charge. 
Plant   Lift    History   Investigations,  Walter  T.   Swingle,    Physiologist    in  Chat 
Cation   Breeding   Investigations,   Archibald    D.   Shame)    and    Daniel   N.   Shoemaker,    physi- 
ologists in  Charg 

investigations,    Archibald    D.    Shamel,    Wightman    W.    Garner,    and    Ernest    II 

Mathewson,   in   Charge. 
Col      l7ivcstigations,  Charles  P.  Hartley,   Physiologist   in  Charge. 

.ml  Drought   Resistant  Plant   Breeding  Investigations,  Thomas   II.  Kearney,   Physi- 

ologist    in    Charge. 
Soil    Bacteriology    and    Water    Purification    Investigations,    Karl    F.    Kellerman,    Physlolo 

in  Charge. 
Bionomic  Investigations   of   Tropical  and  Subtropical  Plants,  Orator   F.   Cook,    Bionomist 

in  Charge 
Drug  and  Poisonous  Plant  and  Tea  Culturi  •lions.  Rodney  II.  True,    Physiologist 

in  Charge. 
Physical  Laboratory,  Lyman  .1.  Briggs,  Physicist  in  Charge. 
Agricultural  Technology,  Nathan   A,  Cobb,  Crop  Technologist    in   Charge 
Taxonomic  and  Rangi   Investigations,  Frederick  V.  Coville,  Botanist   iii  Charge. 
Farm   Management,  William  J.  Spillman,  Agriculturist  in  Charge. 
Grain   Investigations,  Mark  Alfred  Carleton,  Cerealist   in  Charge. 
Arlington    Experimental    Farm    und    Horticultural    Investigatioi    .    I    ■     C.    Corbett,    ll.irti- 

culturist   in  Charge 
VegetabU    Testing  Gardens,  William  W.  Tracy,  sr.,  Superintendent. 
Sugar-Beet   Investigations,  Charles  0    Townsend,    I'athologisl    in   Charge. 
H'i    tern    \in  ii  nil  in  a/   Extension,  Carl  S.   Scofield,    Agriculturist   in   Charge 
Dry-Land    Vgriculturi    Investigations,   E.  Channing  chile. 11.  Agriculturist   in  Charge. 
Pomological  Collections,  Gustavus   B.   Brackett,  Pomologist   in  Charge. 
Field  Investigations  in   Pomology,  William  A.   Taylor  and  G.    Harold   Powell,    P ogists 

in  Charge. 
Experimental  Gardens  and  Grounds,  Edward  M.   Byrnes,  Superintendent. 
Foreign   Seed  and  Plant   Introduction,  David   Fairchild,   Agricultural    Explorer  in  Charge. 
fun,, 1,    cop   Investigations,  Charles   V.    Piper,    Agrostologist    in   Charge 
Seed   Laboratory,   Edgar   Brown,    Botanist    in   Charge 
Grain  Standardisation,  John  1  >.  Shanahan,  1  cop    fochnologist  in  Chargi 
Subtropical  Garden,   Miami,  Fla.,  P.  .1.  Wester,  in  Charge. 

Plant  Introduction  Garden,  Chico,  Vol.,  W.  W.  Tracy,   ir      Assistant  Botanist  in  Charge. 
South   Texa     Garden    Brownsville,  Tex.,  Edward  C.  Green,  Pomologist    In  Charge. 

Cooperative  Demonstration    Work,  Seaman   A.  Knapp,  Special   Agent   in  Charge 
Seed   Disti  iimti o,  1    (Directed     i;    1  hiel    of  Bureau),    Lisle   Morrison,   Assistant    in   General 

Charge. 

Editor.  .1.   E.   Rockwell. 

Chit  1    Clerk,   James    E.    Jones. 
[Cir.23] 
0 


B.   P.    I       i"" 


POTATO  DISEASES  IN  SAN  fOAOUIN  COUNTY, 

CALIFORNIA. 


INTRODUCTION. 

During  recent  years  an  important  center  for  vegetable  growing 
has  developed  in  San  Joaquin  County.  Cal..  through  the  reclama- 
tion of  the  lulc  ni-  peat  hind-  in  the  deltas  of  the  San  Joaquin  and 
Sacramento  rivers.  The  potato  is  the  principal  crop,  about  25,000 
ai  r.  -  being  planted.  It  is  also  one  "I'  the  most  profitable  crops  under 
normal  conditions. 

The  agriculture  of  the  region  is  remarkable  for  tin'  large  areas 
under  one  management,  reaching  several  thousand  acre-  in  some 
cases.  Most  id'  the  land  is  cultivated  by  renters  who  arc  not  perma- 
nent residents.  The  tide  land-  lie  for  the  most  part  near  of  below 
the  high-tide  level  of  the  river.  They  were  originally  partially  over 
flowed  and  covered  with  a  dense  growth  of  marsh  plant-,  but  arc 
now  reclaimed  by  the  construction  of  levee?  along  the  river  bank  and 
the  installation  of  pumping  plants  to  remove  the  water.  The  soil 
consists  of  a  deposit  of  several  feet  of  the  peal  formation  locally 
known  as  tide,  which  contain-  a  large  amount  of  organic  matter  only 
partially  decomposed,  formed  by  the  decay  of  rushes,  sedges,  and 
other  plant-  native  to  those  warm  valley  mar-he-.  Under  cultiva- 
tion and  irrigation  this  soil  work-  down  to  a  ven  fine  and  uniform 
texture.  I>nt  i-  at  first  quite  rough  and  lumpy. 

Since  the  rainfall  is  only  about  lo  inches,  irrigation  i-  essential  for 
crop  production  on  these  peat  soils.  Water  for  this  purpose  i-  ad- 
mitted from  the  river  and  distributed  over  the  level  fields  in  small 
ditches  BO  to  V(|  feel  apart.  The  water  passes  quickly  through  the 
loose  peat  soil  until  the  water  table  i-  raised  nearly  to  the  surface, 
making  in  effect  a  system  of  subirrigation.  A-  the  land  lies  too  low 
for  water  to  run  off,  a  system  of  drainage  is  essential.  This  i-  ac- 
complished by  mean-  of  large  pumps  which  discharge  the  water  into 
t he  ri\ it. 

Potatoes  are  planted  in  March  and  April  as  a  rule,  and  are  har- 
vested as  the  market  requires  them,  from  the  la-t  of  September 
through  October  and  Xovember.  While  several  other  crops  are  grown 
on  the  peat  land-,  including  barley,  beans,  onion-,  and  asparagus,  no 


4  POTATO    DISEASES    IX    CALIFORNIA. 

fixed  system  of  rotation  of  crops  is  practiced.  It  is  customary  to 
plant  potatoes  when  the  lands  are  first  cleared,  and  usually  for  two 
or  three  years,  after  which  the  diminished  yield  and  inferior  quality 
of  the  potato  crop  cause  the  land  to  be  put  into  barley  or  beans.  A  fter 
an  interval  of  one  or  more  year-  potatoes  are  again  planted,  since, 
as  this  crop  returns  the  largest  profits,  the  growers  desire  to  plant 
it  a-  continuously  as  possible.  This,  id'  course,  is  not  good  agricull  ural 
pract  ice. 

It  Inn:  been  found  impossible  to  grow  potatoes  continuously  on  these 
peat  lands  in  spite  of  their  apparently  inexhaustible  fertility.  The 
first  crops  grown  after  the  land  i-  reclaimed  are  phenomenally  large, 
•'Win  to  800  bushel-  per  acre,  and  of  good  appearance.  After  the  first 
or  second  year,  however,  the  yield  diminishes  rapidly  and  the  tubers 
become  rough  and  scabby  to  such  an  extent  a-  to  wipe  out  all  profits. 

In  the  summer  of  1908  the  Bureau  of  Plant  Endustry  was  called 
on  to  determine  the  causes  of  this  condition.  An  inspection  of  the 
fields  brought  out  the  fact  that  several  plant  disease-  appear  to  con- 
stitute the  principal  limiting  factor-  in  this  industry.  A  diagnosis 
of  the  troubles,  with  some  suggestions  for  their  treatment,  i-  given 
herewith.  Entirely  adequate  measures  for  their  control  are  not  yet 
a\  ailable,  but  may  perhaps  be  worked  out  by  further  experimentation. 

POTATO   WILT. 
THE    iaisi:    or    "  POTATO-SICK  "    LANDS. 

Idie  principal  cause  of  the  marked  decrease  in  the  yield  of  old 
potato  land  is  the  presence  of  a  fungous  disease,  the  wilt,  or  dry-rot 
(Fusarium  oxysporum  Schlecht.).  The  connection  of  such  a  parasite 
with  the  troubles  experienced  had  not  been  realized  by  the  growers, 
nor  had  the  fungus  been  reported  from  the  Pacific  coast,  but  a  careful 
study  of  it  had  been  made  in  the  east  by  Dr.  Erwin  F.  Smith  and 
Mi-.  Deane  B.  Swingle,"  of  this  Bureau,  who  worked  out  quite  fully 
the  nature  and  cause  of  the  disease  and  the  character  and  life  history 
of  the  fungus  causing  if.  The  wilt  is  apparently  not  as  prevalent 
or  a-  injurious  in  the  Eastern  State-  ;,-  on  the  Pacific  coast,  and 
but  little  work  has  yet  been  done  on  methods  for  controlling  it. 

DESCRIPTION    01     I  ill:    WILT. 

The  effects  of  the  wilt  a-  observed  in  California  are  exactly  as 
described  by  Smith  ami  Swingle  from  plant-  grown  in  the  District 
of  Columbia.  The  disease  first  becomes  noticeable  when  the  plant- 
are  about    a    foot   high,  though   in   mild  cases   it    may   not   appear  nil 


"Bui.    55,    Bureau    of    Planl     Industry,    "The    Drj  Ro1    oJ    Potatoes    Due   to 
Fusarluiu    Oxysporum."     1904. 

I    r.   23] 


POTA  L'O    DISK  \sl  S    l.\     CALIFORNIA.  f> 

near   maturity.     The   leaves   have   a    lighter  green   color  and   slowly 
assume  a  dull,  unhealthy  appearance,  with  a  rolling  or  curling  of  the 

argins.  The  progress  of  the  disease  is  slow.  Gradually  the  tops 
n  lll"'r  '"'  fall  over  and  the  general  etl'ecl  is  of  |)reniature  ripening. 

diseased  plants  are  easily  pulled  up;  the  roots  are  partly  dead 
and  brittle.  The  will  fungus  frequently  appears  on  them  as  a  white 
or  pink  mold,  and  when  the  underground   portion  of  the  stem  is  cut 

aero  -  a  pron iced  hrov  n  discoloration  is  visible.     This  brown  stain  is 

also  found  in  the  branches  leading  to  the  tubers,  and  a  thin  slice  across 
''"'  -!''111  end  of  the  tuber  will  often  reveal  its  presence  there  as  well. 

Examination  of  thin  sections  of  these  browned  stems  under  the 
microscope  shows  the  fungus  to  be  abundant  in  the  water-carrying 
vessels  of  both  underground  stems  and  roots;  where  ii  appear-  a- 
delicate,  colorless  threads,  bearing  tiny  elliptical  spores. 

The  yield  from  diseased  hills  is  greatly  diminished,  particularly  if 
the  attack  begins  early  in  the  season. 

I  in     urn    ROT  or  THE    11  B]  I."-. 

When  the  potatoes  are  dug  there  is  rarely  any  external  evidence  of 
,Ih'  disease  on  them.     The  major  portion  of  the  crop  produced   from 
lilted  plant-  is  nevertheless  infected,  the  fungus  having  entered  the 
tubers  through   their  -terns.      If  these  potatoes  are  stored   in   a   cold 
place,  but  little  change  occur-,  as  the  fungus  requires  warmth  for  its 
development.     When  infected  potatoes  are  kept   in  a  heated  room  or 
outdoors  in  a  warm  climate,  a  dry-rot  soon  develops. 
_As  tne   fungus  spreads  through  the  potato  the  tuber  shrivels,  be- 
ginning at    the   stem    end;    the    inside    becomes   brown    and    light    in 
weight.    Occasionally  bacteria  cause  a.  secondary  soft-rot,  which  pro- 
m>ds  more  rapidly.     An  earh    form  of  (hi-  Fiisarium  <W\  end-rot  is 
frequently  met  with  shortly  after  digging,  and  potatoes  thus  affected 
are  known  to  buyers  a-  •■  jelly  end-."' 
The  presence  of  the  dry-rot    fungus  can  be  detected   in  otherwise 
"ind   tubers  only  by  making  a   thin  -lice  across  the  stem  end  and 
searching  for  the  brown  discoloration.     Such  potatoes  are  not  desir- 
a,)le   for  -eed.  but   are  not   objectionable   for  cooking,  provided  they 
onsumed  promptly  or  kept  in  cold  storage. 


RELATIONSHIP    OF    POTATO    WILT    TO    SIMILAR    DISEASES     l\     OTHER    rROPS. 

The  potato  wilt  belongs  to  a  group  of  diseases  which  play  a  pronii- 

1"'nl   r,'u'  '"   American  agriculture.     It  i-  related  to  the  wilt  diseases 

atermelon,  cowpea,  tomato,  etc.   which   are  common    in 

the    "'armer   sections  of  our  country.     The    watermelon    growers   of 

San   Joaquin   County    haw  had   experiences  similar   to   those   of  the 

23] 


Q  POTATO    DISEASES    IX    CALIFORNIA. 

potato  growers.  Their  soils  become  "melon  sick"  after  a  few  crops, 
the  reason  being  the  presence  of  the  watermelon  wilt  fungus.  The 
cotton  and  cowpea  wilts  of  the  Southern  States  behave  in  the  same 
way.  The  Bureau  of  Plant  Industry  has.  however,  succeeded  in  com- 
bating them  by  developing  wilt-resistant  varieties  that  will  grow  on 
infected  land.  The  Fusarium  will  of  the  tomato,  prevalent  in  Florida 
and  the  Gulf  States  and  in  California  and  the  Southwest,  is  probably 
more  closely  related  to  the  potato  wilt. 

Soil.  FERTILITY  Nor  A   FACTOR   AFFECTING   WILT. 

The  current  explanation  given  by  the  growers  for  the  decreased  pro- 
ductiveness of  old  potato  fields  is  that  the  potato  crop  has  exhausted 
some  particular  element  of  plant  food  that  it  requires.  There  is  no 
evidence,  scientific  or  otherwise,  to  support  this  view.  The  peat  lands 
are  extremely  fertile.  Other  crops  planted  after  potatoes  produce 
a  full  harvest.  If  any  substances  injurious  to  the  potato  were  given 
off  during  its  growth  they  would  he  neutralized  by  the  superabundant 
organic  matter  present.  Fertilizers  applied  to  peal  soils  subject  to 
the  potato  disease  appear  to  have  no  effect.  Finally,  there  is  enough 
of  this  Fusarium  wilt  present  to  fully  explain  the  lessened  yields. 

MANNER    OF    INFECTION    AND    SPREAD. 

The  wilt  fungus  enters  the  plant  from  the  soil  through  the  roots 
or  underground  stem.-.  The  tubers  are  infected  through  their  stem 
ends  or,  rarely,  through  wounds. 

How  the  fungus  spreads  from  field  to  field  is  not  fully  demon- 
strated. Tt  may  he  present  in  nature  in  some  of  these  alluvial  soils. 
It  is  noteworthy  that  soil-  of  this  type  appear  to  be  predisposed  to 
infection.  One  of  the  principal  mean-  by  which  the  wilt  lias  h 
disseminated  is  clearly  by  the  use  of  infected  seed  tubers.  Not  only 
is  the  local  crop  usually  infected,  hut  the  same  wilt  is  very  prevalent 
in  Oregon,  whence  mo-',  of  the  outside  seed  potatoes  are  obtained. 
Unfortunately,  nearly  all  of  the  area  under  discussion  has  become 
infected.  The  problem  for  the  future  is  not  so  much  to  check  the 
spread  of  the  disease  as  to  control  it  where  it  occur-. 

REMEDIAL  MEASVRES   FOR  WILT. 

Disease-  of  the  i.vpe  of  potato  will  are  very  difficult  to  control. 
The  source  of  infection  and  the  seat  of  the  disease  are  underground; 
hence,  spraying  with  fungicides  would  be  ineffective.  There  is  no 
likelihood  that  applications  of  fungicides  to  the  -oil  would  do  any 
good,  and  Dr.  Frwin  F.  Smith'-  experiments  indicated  thai  ferti- 
lizers had  little  or  no  restrictive  effect  on  the  disease. 

[Cir.  -::j 


^SES    IN     «    VL1FORN1A. 


ROTATION     OF    CH<  IPS. 

Experience  has  shown  thai  the  amount  of  infection  diminishes 
when  barley,  beans,  or  other  crops  are  grown.  Potatoes  planted  after 
a  short  rotation  show  much  less  wilt,  and  \\  hile  it  is  doubl  I'ul  whether 
the  disease  run  bo  gotten  rid  of  entirely  by  any  rotation  that  would 
be  adopted  by  San  Joaquin  County  growers,  there  is  no  question  that 
rotation  of  crops  will  continue  to  be  the  principal  preventive  measure 
in  this  district  until  resistant  varieties  are  developed.  The  mo-t 
profitable  length  of  rotation  remains  to  be  determined  by  further 
trials.  Comparisons  should  be  made  of  plots  or  fields  thai  have  been 
one,  two,  three,  and  four  years  in  other  crops  than  potatoes. 

The  relative  value  of  tin  various  crops  in  reducing  the  amount  of 
potato  wilt  is  unknown.  The  fungus  is  thought  not  to  attack  barley, 
bran-,  or  other  vegetables  likely  to  he  grown,  with  the  possible  excep- 
tion of  tomatoes,  which  would  better  be  avoided.  For  the  present. 
the  principal  consideration  in  selecting  rotation  crops  will  be  their 
profitableness.  This  subject  will  be  further  discussed  later  in  this 
Lilai*. 

WILT-RESISTANT    VARIETIES    OF    POTATl 

Dr.  Erwin  F.  Smith  advises  that  an  effort  be  made  to  secure  re- 
sistant -uain-.  a-  he  si\v  indication-  that  some  plant-  in  the  held-  he 
studied  were  resistant.  We  have  as  yet  no  information  concerning 
the  relative  resistance  of  American  varieties,  but  such  tests  should 
be  made  at  once,  a-  well  as  attempts  to  produce  belter  strains  by  bill 
■■I  mu  and  to  breed   new    resistant    seedlings.     The   fact    that    will- 

stanl  varietii  ot cowpeas.  and  watermelons  havi 

cured  i-  an  encouragement  to  enter  the  more  difficult   held  of  potsi 
ling. 

S  WIT  \i!V     MEASl   It]  - 

I  nder  present  conditions  the  entire  quantity  id'  potato  top-  are  left 
in  the  field,  together  with  thousands  of  bushels  of  -mall  and,  scabby 

ttoes  unfit  lor  marketing.  All  this  refuse  affords  a  bn 
place  for  the  wilt  fungus.  In  consideration  of  the  fact  that  the  nexl 
move  of  the  farmer  must  he  to  rotate  crop-  to  get  rid  of  fungous  in- 
fection. ;t  ■  Id  eem  a  logical  precaution  to  cany  oil  and  destroy 
all  vine-  and  cull-  at  once  after  digging.  Ii  must  be  admitted  thai 
there  is  a-  yet  no  evidence  that  this  would  be  profitable,  but  the 
exjjeriment  should  be  undertaken. 

\     IIEAI   ill  1     -:  l  n    -i   l  i  -i  i  . 

I  he  indications  -.wr  thai  most  of  the  pot  a  toe-  In  the  district  referred 
to  are   infected   with    l-'n-aiium    when    planted.      It    i-   reasonable   to 
suppose  that  better  results  would  follow   the  use  of  healtln   seed,  and 
[Clr. 


8  POTATO    DISEASES    IX    CALIFORNIA. 

trials  should  be  made  at  once  to  demonstrate  this.  Search  should  also 
be  made  for  a  satisfactory  source  of  disease  free  seed.  The  Puget 
Sound  country  appears  to  be  the  most  promising  in  this  respect.  If 
local  -ceil  or  Oregon  seed  is  to  be  used,  an  effort  should  be  made  to 
restrict  the  development  of  the  Fusarium  by  storing  the  seed  potatoes 
in  a  well-ventilated  house  at  a  temperature  of  about  40    F. 

POTATO   SCAB. 

Seal),  a  disease  causing  rough,  pitted  tubers,  is  very  prevalent  in 
California,  where  it  is  considered  the  most  serious  enemy  of  the  crop, 
since  its  injuries  arc  brought  conspicuously  to  the  attention  of  the 
grower  by  the  enforced  rejection  of  the  scabby  potatoes. 

LOSSES  I'lldM   sc  \n. 

The  loss  from  scab  i-  very  heavy.  There  is.  in  the  first  place,  a  re- 
dui  tion  of  yield  due  to  the  attack  of  this  fungus  on  the  underground 
portions  of  the  plant,  and.  seqpndly-j  :'  depreciation  in  quality.  The 
\er\  scabby  potatoes  are  not  marketable,  and  usually  have  to  be  left 
in  the  held,  as  there  is  at  present  uo  starch  or  alcohol  factory  to  utilize 
the  culls.  The  writer  has  roughly  estimated  that  from  5  to  75  per 
cent  of  the  crops  are  rejected  on  account  of  scab,  the  lowest  amounts 
being  found  on  land  planted  for  the  first  time  in  potatoes,  and  the 
highest  on  old  land.  Possibly  25  per  cent  is  an  average  loss  on  land 
previously  planted  to  potatoes.  As  the  annual  production  of  potatoes 
in  San  Joaquin  County  is  more  i  hum  2,500,000  -nek-,  the  loss  from  i  his 
disease  might  easily  amount  to  over  $300,000  per  annum. 

Two  form--  of  scab  appear  to  occur  in  this  area.  The  indications 
are  that  the  principal  injury  is  caused  by  the  same  disease  that  occurs 
in  the  Pastern  States,  which  has  been  shown  to  be  due  to  a  fungus. 
Oospora  scabies.  There  is  at  present,  however,  a  good  deal  of  another 
fungus,  Rhizoctonia,  to  which  has  been  attributed  a  stem-blighl  preva- 
lent in  heavy  western  soils  and  a  surface  cracking  or  russeting  of  the 

i  llliers. 

CAT  si.    OF    SCAB. 

The  cause  of  the  scab  is  a  minute  parasitic  fungus.  The  disease 
does   not    develop  except    where   this    fungus  is   present.      The   amount 

of  scah  is.  however,  greatly  influenced  by  certain  soil  condition-. 
The  principal  factor  appears  to  be  the  acidity  or  alkalinity  of  the  land. 
The  scab  develops  most  freely  in  an  alkaline  soil  and  is  greatly 
retarded  by  acidity,  in  this  respect  the  San  Joaquin  County  soils  are 
extremely  favorable  to  it-  development.  The  amount  of  moisl lire  also 
exerts  an   influence  on  the  disease;   it   appears  to  be   worse   in   wet 

[Cir.   23] 


POTA  M>    DISEASES    IN     CALIFORNIA.  '.I 

'■■'1  in  wet  soils.  It  is  the  experience  of  growers  that  n 
varies  greatly  in  different  seasons,  yet,  nevertheless,  it  can  be  pre- 
vented b\  excluding  the  germs  of  the  disease. 

l*RE\  l\  I'M  i:     MEAS1   RES    I  in;    SCAB. 

U)  Clean  seed.  The  most  frequent  source  of  infect  ion  lies  in  the 
seed  planted,  and  the  experience  of  eastern  growers  has  Keen  that  bv 
disinfecting  the  seed  and  by  planting  in  land  free  from  scab  a  dean 
"•op  may  be  produced,  it  is  therefore  of  the  greatest  importance* 
thai  those  California  growers  who  have  land  not  already  infected  b\ 
this  disease  should  seek  to  keep  it  healthy  by  allowing  nothing  but 
disinfected   seed   to  be   planted. 

I"  the  majority  of  cases,  however,  it  is  necessary  to  deal  with  land 
iIk"  h»s  already  been  infected  h\  the  cultivation  of  one  or  more 
potato  crops.  The  disease  has  already  been  introduced:  the  problem 
lm"  u>  control  it.  It  goes  without  saying  that  additional  rein- 
11,111  should  be  avoided  by  disinfecting  all  the  seed  planted,  in 
accordance  with  directions  given  later  in  this  publication.  Additional 
means  to  be  adopted  comprise : 

(2)  Rotation  of  crops.  Scab  tends  to  diminish  when  land  is 
planted  in  crops  which  do  not  harbor  the  parasite.  Other  root  crops, 
however,  such  as  sugar  beets,  turnips,  etc.,  must  be  avoided.  The 
'ength  of  time  required  to  i'rrr  land  from  scab  varies  in  different 
sections,  but,  as  a  ride,  a  period  of  three  years  will  very  greatly  reduce 
the  amount  of  disease,  though  it  may  not  be  entirely  exterminated 
a  Iter  five,  or  even  ten,  vears. 

The  principal  point  to  be  kepi  in  mind  in  choosing  rotation  crops 
is  "'  increase  the  amounl  of  organic  acids  in  the  soil  by  plowing 
under  green  crops,  such  as  rye,  clover,  vetch,  etc.,  which  by  their 
decay  tend  to  produce  an  acid  reaction  in  the  soil.  It  is  possible  that 
,lu'  soil  can  be  further  favorably  modified  by  the  use  of  fertilizers. 
RUch  ;'^  acid  phosphate,  muriate  of  potash,  land  plaster,  etc..  which 
leave  an  acid  residue.  It  seems  at  first  thought  illogical  to  advise 
plowing  under  ere,.,,  crop,  on  soils  largely  made  up  of  organic  mat 
ter  and  to  suggest  fertilizers  where  there  appear-  to  be  no  lack  of 
plant  food.  No  Mid,  positive  recommendation  is  intended,  but  in 
the  absence  of  knowledge  of  the  subject  such  experiments  to  tesl  this 
should  be  undertaken.  The  beneficial  effect  of  such  treatment  is  well 
recognized  in  the  Eastern  States. 

(3)    Soil  treatment.     The  chemical  treatment  of  the  soil  to  reduce 
promises  but  little.     Applications  of  sulphur  at  the  rale  of  3i 
pounds  per  acre  have  been  used  with  some  degree  of  success  in   Del 
ware  and  New  Jersey  and  might  give  good  results  in  California. 

[Cir.    23] 


10  POTATO    DISEASES    IX    CALIFORNIA. 

SEED   TREATMENT    FOE   m  All." 

The  most  effective  method  of  disinfecting  seed  potatoes  is  by 
the  use  of  formaldehyde  gas  liberated  by  mixing  the  commercial 
solution  with  potassium  permanganate.  This  method  is  adapted 
to  the  disinfection  of  large  quantities  of  potatoes  in  a  short  time. 
To  use  it.  an  air-tight  shed  should  he  constructed  of  sufficient 
size  to  hold  whatever  quantity  it  may  lie  desired  to  treat  at  one  lime. 
This  may  he  made  of  rough  lumber,  lined  with  building  paper  and 
provided  with  a  tight  door.  The  potatoes  may  lie  treated  in  sacks, 
hut  these  sacks  must  be  piled  so  as  to  allow  a  free  circulation  of  air 
all  around  them.  It  is  suggested  that  they  he  piled  in  tiers,  with  two 
2  by  4  inch  scantlings  between  each  layer  of  sacks.  Space  should  be 
left  in  the  center  of  the  building  for  placing  the  charge  of  formalde- 
hyde, which  should  he  set  oil'  in  shallow  pans,  such  as  galvanized 
washtubs.  For  each  1,000  cubic  feet  •_;:;  ounces  of  potassium  per- 
manganate and  ."J  pints  of  formaldehyde  should  he  allowed.  After 
the  potatoes  are  properly  slacked  and  everything  is  made  ready,  the 
permanganate  should  lie  spread  in  a  thin  layer  on  the  bottom  of  the 
pan.  the  required  quantity  of  formaldehyde  poured  in  and  stirred 
quickly,  and  the  building  vacated.  The  building  should  then  he  kept 
closed  tight  for  twenty-four  hours,  when  it  may  be  opened  and  the 
potatoes  taken  out. 

Formaldehyde  i-  a  nonpoisonous  hut  highly  irritant  fluid  which 
can  be  purchased  in  -mall  lots  at  about  50  cents  a  pound,  in  carboy 
lots  at  20  cents,  or  in  barrel  lots  at  about  12  cent-.  Potassium  per- 
manganate is  a  reddish  brown,  crystalline  substance,  purchasable  at 
from  13  to  25  cent-  a  pound. 

The  precaution  should  be  taken  not  to  pile  any  potatoes  directly 
over  the  pans  or  within  3  feet  laterally,  as  the  gas  there  mighl  he 
strong  enough  to  injure  the  potatoes  and  destroy  their  germinating 
power.  The  formaldehyde  works  best  in  a  humid  atmosphere.  It  i- 
therefore  advised  that  the  floor  of  the  shed  !»•  wet  down  before  the 
treatment  i-  made.  The  potatoes,  however,  should  not  he  wet.  i-  the 
disinfection  is  more  thorough  if  the  surfaces  are  dry. 

Small  quantities  of  potatoes  may  he  disinfected  by  soaking  in  a 
solution  of  1  pint  id'  formaldehyde  to  .",(>  gallons  of  water  for  two 
hours.  Either  the  gas  or  the  solution  treatment  may  he  applied  some 
time  previous  to  planting,  provided  the  potatoes  are  not  exposed  to 
reinfection  by  being  put  into  receptacle-  that  have  previously  held 
scabby   potatoes.     The   treatment    should    also   he   made   befor<    the 

potatoes  arc  cut    for  -eed. 

"Adapted  from  Bulletins   lit   and    tin.   Maine  Agricultural   Experinienl   sta- 
tion, by  \V.  .1.  Morse. 
23] 


1M  .  I  aim    DISI  \.->  S    IX    CALIFOBK  IA.  II 


i  dm    ui     SKKD    i  1:1    v  I  \i  I  \  I . 


I  i.  expense  connected  with  the  treatmenl  of  seed  potatoes  b\  the 
gas  method  will  vary  in  different  cases  according  to  the  amount  of 
labor  required  in  handling  and  whether  a  special  building  has  to  be 
erected  for  the  purpose.  The  cost  of  labor  and  of  the  building  will 
be  the  principal  items.  The  cost  of  the  materials  need  not  amount 
in  over  1  cent  pei  sack.  For  example,  a  shed  \-2  by  _l  feet  and  7 
feet  high  contains  2,01G  cubic  feet  and  would  require  '■)  pounds  of 
potassium  permanganate,  costing  GO  cents,  and  C>  pints  of  formalde- 
hyde, costing  $1.20;  total.  $1.80.  Two  hundred  sacks  can  easily  be 
treated  at  once  in  such  a  shed.  An  entire  day  should  be  allowed  for 
each  treatment. 

DECAY  OF  POTATOES. 

Considerable  loss  is  occasionallj  experienced  from  the  rapid  decay 

of  potatoes  short h    after  harvesting.     It   is  reported  that   an  entire 

shipment   of  potatoes  will  sometimes  '*  go  down"  in  a    few    day-  or 

while   en    route    to    market.     This   trouble   is   locally    known    by    the 

issive  term  "  leak."  or  "  melters." 

The  affected  potatoes  turn  a  dull  brown  outside;  the  flesh  i-  buff  or 
brown  and  very  soft.  When  subjected  to  pressure  a  copious  amount 
of  clear  brown  liquid  is  discharged.  There  is  no  bad  odor  in  the 
early  stages. 

CAT  SE  oi     I  HE  ""  l.liAK." 

This  form  of  decay  is  due  to  the  invasion  of  a  fungus.  RJtizopus 
cans.  This  fungus  can  enter  only  through  wounds,  and  experi- 
ments in  the  laboratory  have  corroborated  the  testimony  of  the  grow- 
er- that  potatoes  injured  by  careless  digging  especially  are  attacked. 
The  fungus  spreads  rapidly  under  favorable  conditions,  growing 
between  the  cell  walls.  Later  the  cells  are  separated,  and  hence  the 
rapid  softening  of  the  tissue. 

The  fungus  i-  propagated  by  -pore-  produced  in  large  heads  or 
sporangia.  It  can  grow  on  a  great  variety  of  dead  organic  substances. 
AYhile  it  is  not  usually  considered  a  dangerous  parasite,  it  is  known 
to  cause  decay  in  sweet  potatoes,  apples,  and  pear-,  and  a  related 
fungus  causes  a  disease  of  lily  bulbs. 

Ill   \|  EDIA]      M  I    \-l   RES    I  '  IK    THE   "  LEAK.*' 

for   the  control  of  this  disease  may  be  based  on  our 
know  ledge  of  it-  cause  : 

Avoid   breaking  the  skin  of  the  potato  in  handling.     Nature 
has  given  the  potato  an  effective  protection  against  such   fungi  in  an 
unbroken  epidermis.     Rhizopus  is  a  wound  parasite,  and   fork  holes 
and  bruises  are  it-  principal  mean-  of  entrance. 
23] 


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14  POTATO    DISEASES    IN    CALIFORNIA. 


\1.I  ALFA. 


Experimental  plantings  of  alfalfa  made  at  Middle  River  have  suc- 
ceeded well.  In  the  light  of  these  experiments  ii  seems  probable  that 
alfalfa  will  do  well  on  the  peat  lands  where  the  water  is  not  allowed 
to  come  too  near  the  surface.  The  use  of  alfalfa,  however,  would 
probably  necessitate  leaving  the  land  in  this  crop  for  several  years, 
which  might  be  desirable  where  the  land  had  become  badly  infested 
with  potato  diseases. 

Among  the  varieties  tested  at  Middle  River  the  Arabian  variety 
was  decidedly  better  than  any  other.  On  November  11.  1908,  a  few 
weeks  after  the  last  cutting  of  all  of  the  plots,  the  Arabian  alfalfa 
was  12  inches  high,  while  the  ordinary  alfalfa  had  made  scarcely  any 
growth.  This  ability  of  the  Arabian  alfalfa  to  grow  during  the  cool 
weather  of  late  fall  and  early  spring  would  be  particularly  valuable 
from  the  standpoint  of  winter  pasturage. 


OTHER    FOB  Ml      I  ROPS. 

Doubtless  many  other  forage  crops,  both  legumes  and  grasses, 
would  succeed  on  the  peat  lands.  Experimental  plantings  of  a  large 
number  will  be  made.  The  list  of  those  that  are  known  to  be  suc- 
cessful on  these  lands  is  sufficient,  however,  to  meet  present  needs, 
and  the  knowledge  of  each  is  so  definite  that  no  farmer  need  hesitate 
to  plant  those  recommended  in  these  pages. 

Approved  : 

James  Wilson. 

St  cretary  of  .  I  grieidturt . 

Washington,  D.  ('..  January  .'',  1909. 

[Cir.  28] 

o 


UNIVERSITY  OF   FLORIDA 


3  1262  08928  9663 


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